The invention relates to a process for operating an open-end friction spinning machine having a plurality of spinning units that each comprise a friction zone formed by two friction surfaces moving in opposite directions that is used as a yarn forming point. Each spinning unit also includes a feeding and opening device for the feeding of fibers to the friction zone, a suction device for holding the fibers and the forming yarn in the friction zone and a withdrawal device for withdrawing the yarn from the friction zone. The respective existing friction effect is monitored.
In a known process shown in DE-OS No. 33 42 481, the friction effect at each individual spinning unit, as well as between the respective spinning units with respect to one another, is kept as equal as possible so that a yarn is spun of a quality that is as uniform as possible. The friction effect significantly influences the quality of the spun yarn. Changes of this friction effect, essentially the coefficient of friction of the friction surfaces and the air current generated by the suction device, results immediately in a change of the quality and structure of the yarn. By examination of the friction effect, it is therefore endeavored to recognize changes in time and, if necessary, take appropriate measures so that a yarn quality can be achieved that is as uniform as possible.
One object of the invention is to provide a process of the initially mentioned type in which an informative monitoring of the friction effect is achieved as simply as possible.
This object is achieved by determining at least a part of the friction effect separately for the two friction surfaces of one spinning unit and comparing this effect between surfaces.
The invention is based on the recognition that it is sufficient for an informative monitoring to determine a change in the ratio of the friction effects of the two friction surfaces without the requirement of an exact measurement of the friction effect that refers to a basic quantity. As a result, it is possible to considerably reduce the equipment required for determining the friction effect, particularly with respect to forces to be applied and/or precisions to be observed when measuring devices are applied. The invention is also based on the recognition that, on the one hand, it cannot be expected that the friction effects will change in an identical way at both friction surfaces, and an inadmissible change of the ratio is a clear indication of an inadmissible change of the overall friction effect. On the other hand, it can be assumed that should the friction effects change in an identical way, this would only have a minor effect on the quality of the spun yarn, as long as a certain limit is not exceeded.
In the case of a further development of the invention, it is provided that the two friction surfaces, at least over a part of the length of the friction zone, are designed for different friction effects. In an advantageous further development, it is provided in this case that the friction surfaces form wedge-shaped gap type friction zone and that the friction surface that moves out of the wedge-shaped gap, at least over a part of the length of the wedge-shaped gap, is designed for a friction effect that is increased with respect to the other friction surface. This different design of the friction effect is naturally taken into account during the monitoring. In practice, it was found that the differences in the friction effects of the friction surfaces should be between 5% and 25%, in which case an optimum is in the range of 15%. Since the friction effects are composed of the coefficient of friction of the surfaces of the friction areas and of the force of the air flow generated by the suction device, the coefficient of friction of the surfaces of the friction areas and/or the amount of the air flow can be designed correspondingly. As a rule, it is advisable to construct the surfaces of the friction areas with a different coefficient of friction and to consider the apportioning of the air flow only as a correction and an adjustment.
In a further development of the invention, it is provided that the friction effect existing in circumferential direction of the forming yarn and the friction effect existing in withdrawal direction of the forming yarn are determined. The friction effect acting in circumferential direction of the forming yarn is essentially responsible for the yarn twist, whereas the friction effect existing in withdrawal direction of the forming yarn is largely responsible for the tension of the yarn. Both values may be indicators of the spinning stability of a spinning unit.
In a further development of the invention, it is provided that a part of the friction effect is determined by an examination of the surface structure of the friction areas. This examination of the surface structure supplies information on any change of the coefficient of friction of the friction areas on the basis of a change of the surface structure. This examination of the surface structure may be carried out by means of optical sensors or picture recognition systems that offer the advantage of a non-contact examination.
In a further development of the invention, it is provided that a part of the friction effect is determined by an examination of the coefficient of friction at the surfaces of the friction areas. In this case, it may, for example, be provided that a measuring element in the form of a measuring string, a measuring yarn, a strip of woven fabric or knitted fabric, or the like is guided over the surface of the friction areas. In this embodiment, the measuring element is held in such a way that the take-along force which is applied to this measuring element because of the friction can be measured. In this case, it is advantageous to provide this measuring element in the form of a spool or of a reserve receptacle so that for each of the measurements, an unused part of the measuring element is available that has not been changed by preceding measurements.
In a further development of the invention, it is provided that a part of the friction effect is determined by examining the suction effect of the suction device. In the case of this development, a probe is brought into the range of the two friction areas by means of which a measurement is carried out of the vacuum and/or of the amount of air flowing in the range of the two friction areas.
In a further development of the invention, it is provided that the friction effect is determined by examining the spun yarn. This examination has the advantage that it can be carried out during the uninterrupted spinning process. Therefore, a conclusion can be drawn to the friction effect from the changes of the yarn diameter and/or the yarn structure. For example, in the case of a change of the diameter of the yarn, a conclusion can be drawn on the provided twist, which is dependent on the friction effect. In this case, however, the proportion of the friction effect of both friction areas is not detected. Therefore, it is advantageous to use this determination of the friction effect by examining the yarn in combination with and subsequent to one of the other types of determinations when a change is determined by examining the yarn.
In a further development of the invention, it is provided that the friction effects are determined by a device that can be moved along the spinning machine and that can be applied to the individual spinning units. This type of movable device has the advantage that only one monitoring device for determining the friction effect or parts of the friction effect is required. Therefore, individual monitoring devices do not have to be provided at each spinning unit. Obviously, individual monitoring devices can be provided at each spinning unit, but usually results in higher expenditures. Since only the relative changes of the friction effect between the two friction areas are determined, the requirements concerning the precision of the elements of the movable device, and especially with respect to its adjustment, are not too high because these can be applied without difficulty in such a way that they can be brought into the range of both friction areas with sufficient precision.
In the case of a further simple embodiment of the invention, it is provided that the determined values are displayed in a way that can be recognized by an operator. Advantageously, these values are stored and can be retrieved by the operator. The operator will then have to decide whether corrections must be carried out at the spinning units.
In a further development of the invention, it is provided that at least a part of the friction effect of the friction areas is corrected by an automatically operating device when a determined deviation exceeds a permissible value. The correction is a function of this deviation. Thus a correction will no longer depend on the attention, the care and the skill of the operator.
In a further development of the invention, it is provided that the correcting of the friction effect is carried out by treating at least one friction area. This type of treatment may, for example, include a changing of the surface by grinding, brushing or grinding with emery paper, or the like. It is also possible to provide a pneumatic-mechanical treatment during which small particles of sand or glass are thrown against the friction areas by means of an air flow. A device to be used for this purpose must naturally, by means of baffle plates or the like, be developed in such a way that the particles thrown back from the surfaces of the friction areas are collected and removed. The treatment of the surfaces of the friction areas may also be carried out by means of a fluid containing solid components. In addition, it is possible to treat the surfaces by chemical means that are applied in powder, liquid or paste form and are subsequently wiped off by means of a cleaning roller or the like. With this type of treatment, a cleaning and/or etching, and roughening of the surfaces can take place.
For the after-treatment of the friction areas, an electric eroding may also be provided. In addition, it is possible to dust the surfaces of the friction areas with a powder that completely or partially adheres to the surfaces, and thereby close the pores or furrows or the like of these surfaces, which affects the coefficient of friction. As a treatment, a washing-off of the friction areas may also be carried out to remove any deposits on the surfaces which were deposited during the spinning. This washing-off, which removes cotton wax or the like, for example, is advantageously combined with a mechanical brushing-off and a subsequent drying. In addition, it is possible to change the coefficient of friction corresponding to the determined deviations, by means of a heat treatment of the surfaces of the friction areas. Naturally, it is also possible without difficulty to combine one or several of the above-described types of treatment with one another.
In a further development of the invention, it is provided that the correcting is carried out by the adjusting of a spinning parameter influencing the friction effect. In this development, it is provided that for the correcting, the suction effect of the suction device onto at least one friction surface is changed. This type of correction has the advantage that it can be carried out very rapidly and without problems, without having to carry out costly work at the spinning unit. The changing of the suction effect may be carried out via control valves or by changing the suction slots of the suction inserts facing the friction areas. These suction slots may be changed with respect to their position and/or their penetration cross-section.
In the case of another development, it is provided that for the correcting, the moving speed of at least one friction area is changed. Naturally, the moving speed of the friction areas has an influence on their friction effect. However, a correction via the moving speed is possible only if the friction areas are driven by means of independently controllable drives, for example by two individual motors.
After all types of corrections are made, it is advisable to make another examination of the friction effect or of the measured part so that the result of the correction can be checked. The examining of the friction effect may take place at periodic intervals, or also at certain operating conditions of the concerned spinning unit, for example, in the case of a yarn breakage or a spool change. In this case, the measuring in a particularly advantageous development is carried out while the machine is running, in which case the concerned spinning unit itself may be stopped. In this case, it is possible to drive the friction areas at a speed that is suitable for measuring, particularly by means of an auxiliary drive of the movable device. It is also possible to carry out the examination of the friction areas during the spinning operation. For example, via an opening, the corresponding measuring elements can be applied to the friction areas outside the range of the friction zone serving as the yarn forming point.
Other characteristics and advantages of the invention are found in the following description of the embodiments shown in the drawings.